ABSTRACT Websites selling alcohol have undermined progress made in the offline world to reduce youth alcohol use and access, but have received relatively little legislative attention compared to Internet Tobacco Vendors (ITVs), now regulated by many state and federal laws. ITVs and Internet Alcohol Vendors (IAVs) share a primary public health concern; youth access; 92%-100% of ITVs fail to properly verify buyers' ages. In the P.I.'s studies of IAVs in 2010-2011, about half sold to minors, often leaving alcohol at buyers' doors without age verification. While youth access is a substantial concern with IAVs, the little regulatory attention given to this $2.4 billion a year industry has focused on allowing interstate wine shipment from vineyards. The P.I.'s 2010 research identified over 5,000 IAVs, over 6 times as many as the number of Internet Cigarette Vendors identified at that industry's apex. Since 2011, there has been no additional research on youth access to alcohol from IAVs or recently introduced alcohol delivery apps. The scant research about online alcohol marketing to minors published since relies on pre-2013 data. Clearly, there is a large population of IAVs, and historically, their practices have not adequately prevented sales to minors. There is a critical need for more research investigating youth's exposure to online alcohol marketing, youth access to alcohol via online vendors and smartphone apps, and current IAV youth access prevention practices need to be documented to inform policy and track improvements in the industry's practices over time. National studies that investigate teens' sources of alcohol have never included Internet as a potential source, so the current proportion of teens who buy alcohol online is unknown. The innovative proposed research includes a survey to assess in-depth teen and young adult alcohol and substance use and extent of use and exposure to IAVs and delivery apps. Further, it will include an updated youth purchase study from IAVs. Informed by survey and purchase study findings, a theory-driven IAV intervention (evaluated with a follow-up purchase study) will encourage improvements in youth access prevention practices, and will assess whether, as the FTC suggests, the alcohol industry is willing and able to self-regulate. Our long-term goal is to provide the foundation for R01 funding to further study youth exposure and access to alcohol (and its marketing) online and via delivery apps, to evaluate on a broad scale intervention approaches to improve vendor self-regulation, and in the absence of self-regulation, to assess whether a similar regulatory framework to that which was developed by the P.I. and applied to Internet tobacco sales can be effective with online alcohol sales to reduce youth access. Our overall objective for this study, which is the next step toward attainment of our long-term goal, will have significant impact by using state-of-the-art methods to assess IAVs' youth access prevention practices, the extent and correlates of teen and young adult drinkers' exposure to online alcohol marketing and sales, as well the effectiveness of an intervention to influence the IAV industry to self-regulate to improve youth access prevention.